In a large pot of boiling, salted water, cook the orzo until al dente; drain and return to the pot. Stir in the pine nuts, parsley, lemon juice, lemon peel and 2 tablespoons extra-virgin olive oil; season with salt and pepper. In a skillet, heat 1/4 cup olive oil over high heat until rippling. Add the mushrooms and cook, stirring occasionally, until browned, about 7 minutes. Divide the orzo among 4 plates and top with the mushrooms.